Abstract
Human ether-à-go-go-related gene 1 (hERG1) channels conduct the rapid delayed rectifier K+ current, IKr, an important determinant of action potential repolarization in mammals, including humans. Reduced IKr function caused by mutations in KCNH2 or drug block of hERG1 channels prolongs the QT interval of the electrocardiogram and increases the risk of ventricular fibrillation and sudden cardiac death. Several activators of hERG1 channels have been discovered in recent years. These compounds shorten the duration of cardiac action potentials and have been proposed as a new therapeutic approach for the treatment of acquired or congenital long QT syndrome. We defined previously the mechanism of action of 1,3-bis-(2-hydroxy-5-trifluoromethyl-phenyl)-urea (NS1643), a compound that increases hERG1 currents by shifting the voltage-dependence of inactivation to more positive potentials. Here, we use scanning mutagenesis of hERG1 and functional characterization of 56 mutant channels heterologously expressed in Xenopus laevis oocytes to define the molecular determinants of the binding site for NS1643. Most point mutations did not alter response to the drug; however, 10 mutant channels had reduced sensitivity, and F619A and I567A exhibited enhanced activation by the drug. Some of these residues form a cluster and, together with molecular modeling, suggest that NS1643 binds to a pocket near the extracellular ends of the S5/S6 segments of two adjacent hERG1 channel subunits. This putative binding site differs from the sites described previously for two other hERG1 activators, (3R,4R)-4-[3-(6-methoxy-quinolin-4-yl)-3-oxo-propyl]-1-[3-(2,3,5-trifluoro-phenyl)-prop-2-ynyl]-piperidine-3-carboxylic acid (RPR260243) and 2-(4-[2-(3,4-dichloro-phenyl)-ethyl]-phenylamino)-benzoic acid (PD-118057).
Footnotes
This work was supported by The Danish National Research Foundation Centre for Cardiac Arrhythmia; The Novo Nordisk Foundation; The Aase and Ejnar Danielsen Foundation; The National Danish Research Council; and the National Institutes of Health National Heart, Lung, and Blood Institute [Grant HL055236].
M.G. has minor-equity holdings in NeuroSearch A/S. The other authors have no potential conflicts of interest.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.067728.
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ABBREVIATIONS:
- hERG1
- human ether-à-go-go-related gene type 1
- LQT2
- long QT syndrome type 2
- NS1643
- 1,3-bis-(2-hydroxy-5-trifluoromethyl-phenyl)-urea
- RPR260243
- (3R,4R)-4-[3-(6-methoxy-quinolin-4-yl)-3-oxo-propyl]-1-[3-(2,3,5-trifluoro-phenyl)-prop-2-ynyl]-piperidine-3-carboxylic acid
- PD-118057
- 2-(4-[2-(3,4-dichloro-phenyl)-ethyl]-phenylamino)-benzoic acid
- PD-307243
- 2-[2-(3,4-dichloro-phenyl)-2,3-dihydro-1H-isoindol-5-ylamino]-nicotinic acid
- NS3623
- N-(4-bromo-2-(1H-tetrazol-5-yl)-phenyl)-N′-(3′-trifluoromethylphenyl)urea
- ICA-105574
- 3-nitro-N-(4-phenoxyphenyl) benzamide
- A-935142
- {4-[4-(5-trifluoromethyl-1H-pyrazol-3-yl)-phenyl]-cyclohexyl}-acetic acid
- WT
- wild type.
- Received July 22, 2010.
- Accepted September 27, 2010.
- Copyright © 2011 The American Society for Pharmacology and Experimental Therapeutics
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